/*    $OpenBSD: qsort.c,v 1.18 2017/05/30 14:54:09 millert Exp $ */
/*-
 * Copyright (c) 1992, 1993
 *    The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

//#include <sys/types.h>
//#include <stdlib.h>

#include "qsort.h"

static __inline char    *med3(char *, char *, char *, int (*)(const void *, const void *));
static __inline void     swapfunc(char *, char *, size_t, int);

#define min(a, b)    (a) < (b) ? a : b

/*
 * Qsort routine from Bentley & McIlroy's "Engineering a Sort Function".
 *
 * This version differs from Bentley & McIlroy in the following ways:
 *   1. The partition value is swapped into a[0] instead of being
 *    stored out of line.
 *
 *   2. The swap function can swap 32-bit aligned elements on 64-bit
 *    platforms instead of swapping them as byte-aligned.
 *
 *   3. It uses David Musser's introsort algorithm to fall back to
 *    heapsort(3) when the recursion depth reaches 2*lg(n + 1).
 *    This avoids quicksort's quadratic behavior for pathological
 *    input without appreciably changing the average run time.
 *
 *   4. Tail recursion is eliminated when sorting the larger of two
 *    subpartitions to save stack space.
 */
#define SWAPTYPE_BYTEV    1
#define SWAPTYPE_INTV    2
#define SWAPTYPE_LONGV    3
#define SWAPTYPE_INT    4
#define SWAPTYPE_LONG    5

#define TYPE_ALIGNED(TYPE, a, es)            \
    (((char *)a - (char *)0) % sizeof(TYPE) == 0 && es % sizeof(TYPE) == 0)

#define swapcode(TYPE, parmi, parmj, n) {         \
    size_t i = (n) / sizeof (TYPE);         \
    TYPE *pi = (TYPE *) (parmi);             \
    TYPE *pj = (TYPE *) (parmj);             \
    do {                         \
        TYPE    t = *pi;            \
        *pi++ = *pj;                \
        *pj++ = t;                \
        } while (--i > 0);                \
}

static __inline void
swapfunc(char *a, char *b, size_t n, int swaptype)
{
    switch (swaptype) {
    case SWAPTYPE_INT:
    case SWAPTYPE_INTV:
        swapcode(int, a, b, n);
        break;
    case SWAPTYPE_LONG:
    case SWAPTYPE_LONGV:
        swapcode(long, a, b, n);
        break;
    default:
        swapcode(char, a, b, n);
        break;
    }
}

#define swap(a, b)    do {                \
    switch (swaptype) {                \
    case SWAPTYPE_INT: {                \
        int t = *(int *)(a);            \
        *(int *)(a) = *(int *)(b);        \
        *(int *)(b) = t;            \
        break;                    \
        }                        \
    case SWAPTYPE_LONG: {                \
        long t = *(long *)(a);            \
        *(long *)(a) = *(long *)(b);        \
        *(long *)(b) = t;            \
        break;                    \
        }                        \
    default:                    \
        swapfunc(a, b, es, swaptype);        \
    }                        \
} while (0)

#define vecswap(a, b, n)     if ((n) > 0) swapfunc(a, b, n, swaptype)

static __inline char *
med3(char *a, char *b, char *c, int (*cmp)(const void *, const void *))
{
    return cmp(a, b) < 0 ?
           (cmp(b, c) < 0 ? b : (cmp(a, c) < 0 ? c : a ))
              :(cmp(b, c) > 0 ? b : (cmp(a, c) < 0 ? a : c ));
}

static void
introsort(char *a, size_t n, size_t es, size_t maxdepth, int swaptype,
    int (*cmp)(const void *, const void *))
{
    char *pa, *pb, *pc, *pd, *pl, *pm, *pn;
    int cmp_result;
    size_t r, s;

loop:    if (n < 7) {
        for (pm = a + es; pm < a + n * es; pm += es)
            for (pl = pm; pl > a && cmp(pl - es, pl) > 0;
                 pl -= es)
                swap(pl, pl - es);
        return;
    }
    if (maxdepth == 0) {
        if (heapsort(a, n, es, cmp) == 0)
            return;
    }
    maxdepth--;
    pm = a + (n / 2) * es;
    if (n > 7) {
        pl = a;
        pn = a + (n - 1) * es;
        if (n > 40) {
            s = (n / 8) * es;
            pl = med3(pl, pl + s, pl + 2 * s, cmp);
            pm = med3(pm - s, pm, pm + s, cmp);
            pn = med3(pn - 2 * s, pn - s, pn, cmp);
        }
        pm = med3(pl, pm, pn, cmp);
    }
    swap(a, pm);
    pa = pb = a + es;
    pc = pd = a + (n - 1) * es;
    for (;;) {
        while (pb <= pc && (cmp_result = cmp(pb, a)) <= 0) {
            if (cmp_result == 0) {
                swap(pa, pb);
                pa += es;
            }
            pb += es;
        }
        while (pb <= pc && (cmp_result = cmp(pc, a)) >= 0) {
            if (cmp_result == 0) {
                swap(pc, pd);
                pd -= es;
            }
            pc -= es;
        }
        if (pb > pc)
            break;
        swap(pb, pc);
        pb += es;
        pc -= es;
    }

    pn = a + n * es;
    r = min(pa - a, pb - pa);
    vecswap(a, pb - r, r);
    r = min(pd - pc, pn - pd - es);
    vecswap(pb, pn - r, r);
    /*
     * To save stack space we sort the smaller side of the partition first
     * using recursion and eliminate tail recursion for the larger side.
     */
    r = pb - pa;
    s = pd - pc;
    if (r < s) {
        /* Recurse for 1st side, iterate for 2nd side. */
        if (s > es) {
            if (r > es) {
                introsort(a, r / es, es, maxdepth,
                    swaptype, cmp);
            }
            a = pn - s;
            n = s / es;
            goto loop;
        }
    } else {
        /* Recurse for 2nd side, iterate for 1st side. */
        if (r > es) {
            if (s > es) {
                introsort(pn - s, s / es, es, maxdepth,
                    swaptype, cmp);
            }
            n = r / es;
            goto loop;
        }
    }
}

void
qsort(void *a, size_t n, size_t es, int (*cmp)(const void *, const void *))
{
    size_t i, maxdepth = 0;
    int swaptype;

    /* Approximate 2*ceil(lg(n + 1)) */
    for (i = n; i > 0; i >>= 1)
        maxdepth++;
    maxdepth *= 2;

    if (TYPE_ALIGNED(long, a, es))
        swaptype = es == sizeof(long) ? SWAPTYPE_LONG : SWAPTYPE_LONGV;
    else if (sizeof(int) != sizeof(long) && TYPE_ALIGNED(int, a, es))
        swaptype = es == sizeof(int) ? SWAPTYPE_INT : SWAPTYPE_INTV;
    else
        swaptype = SWAPTYPE_BYTEV;

    introsort((char *)a, n, es, maxdepth, swaptype, cmp);

}

//DEF_STRONG(qsort);
